1. The Field of the Invention
The present invention relates to a method and apparatus for positioning core samples for x-ray computed tomography measurements and in particular to a method and apparatus which will repeatedly accurately position such core samples.
2. The Prior Art
Computerized axial tomographic scanners (hereinafter referred to as "CAT" scanners) are well-known devices for providing an image of a sample that has spatial resolution in the axial direction that is smaller than the width of the x-ray beam. CAT scanners are widely used, for example, in the medical industry to scan a patient in an attempt to diagnose various medical problems. The patient is supported on a table that moves the patient through the scanning device at a controlled rate.
Accurate and repeatable positioning of core samples during x-ray computed tomography measurements is critical for performing many petrophysical measurements such as porosity distributions and fracture direction, size, and porosity. The sample positioning system that is provided with the standard CAT scanner, namely a patient table, is designed for use in positioning people who are relatively much less heterogeneous than rocks. Major requirements for patient tables are the patient comfort and the ability to support patients of varying sizes and weights while repeatability of the positioning for any one patient is much less critical.
The present invention replaces the known patient table with an improved table assembly which mimics all capabilities of the patient table. In addition, it positions a sample for scanning with accuracy and repeatability not theretofore possible. The improvement in accuracy of positioning is by a factor of from one millimeter, in the prior art tables, to 0.02 millimeters for the subject table assembly. The present invention automatically centers the sample to be scanned within a scanning circle thereby alleviating the need to perform numerous test scans heretofore required to verify sample centering. It also eliminates the need for shims or like means to reposition or adjust the position of the sample in order to achieve the desired position. The control means of the present invention is compatible with that of standard CAT scanner hardware and software. This enables the present invention to be readily exchanged for the patient table assembly means commonly provided with a CAT scanner thereby obviating the requirement for even minor modifications in order for the present invention to be used.
The present invention comprises a specialized table assembly which serves as a replacement for the standard patient positioning table of known CAT scanners. Such a patient table is inadequate for supporting and moving geological cores and other non-biological samples, during the actual scanning process.
The subject table is particularly suitable for use with Technicare model 2020HR and 2060 CAT scanners.